Terence Crawford, who became just the third fighter of the four-belt era to unify all of the titles with an electrifying knockout of Julius Indongo in August, vacated his WBO junior welterweight title on Thursday and is now headed up to the 147-pound welterweight division.

Crawford (32-0, 23 KO’s), who is widely considered one of the best pound-for-pound, was also named the mandatory challenger to welterweight world titleholder Jeff Horn at its annual convention, which is taking place aboard a cruise ship in the Caribbean.

The 29-year-old Horn (17-0-1, 11 KO’s), who defeated Manny Pacquiao controversially to take the world title in July, is slated to meet British challenger Gary Corcoran (17-1, 7 KO’s) on Dec. 13, a Wednesday, at Brisbane Convention Centre.

Crawford made his professional debut in 2008 and is a two-division world champion. He took the title away from Ricky Burns in his native Scotland in 2014 and defended the belt twice with impressive victories over Yuriorkis Gamboa and Ray Beltran. Then, Crawford made the jump to 135 pounds and knocked out Thomas Dulorme for a vacant world title in 2015.

Crawford made six defenses, winning five of them by knockout. The only man to go the distance was Viktor Postol. However, the former WBC world champion was dominated and dropped twice en-route to his first professional defeat.

“I think Crawford is an enormous talent,” Bob Arum, Crawford’s promoter of Top Rank, told ESPN. “I know that if he wins the welterweight title, I am going to look to match him with a number of fighters that are managed by Al Haymon, like [former titleholder] Danny Garcia, [unified champion] Keith Thurman, and a huge fight would be one with [IBF champion Errol] Spence. That would be a big pay-per-view fight.”